1. Field of the Invention
This invention relates to a video and audio editing system, and more particularly to an editing system for controlling an external apparatus by means of a personal computer (PC) to select video and audio materials of a required scene and store them as data for a multimedia application.
2. Description of the Related Art
A system which employs, for example, an application software program "Vidcap.exe" which operates on the operating system "Windows 3.1" offered by Microsoft, United States, is known as an editing system which controls an external apparatus by means of a personal computer to select video and audio materials of a required scene and input, compress and store data of them to, by and in the personal computer.
FIG. 10 shows in block diagram a construction of the system mentioned above.
Referring to FIG. 10, the system shown includes a personal computer (PC) 102 including a CPU (Central Processing Unit) 100 and a ROM 101 and an external apparatus 103 connected to the personal computer 102 via a transmission line 104 and an RS232C interface 105. The system further includes an instruction inputting apparatus 106 such as a keyboard or a pointing device by which instructions are entered by an operator, a video board 107 and an audio board 108 for fetching video data and audio data from the external apparatus 103 into the personal computer 102 via transmission lines 104, a memory 109 which is used to compress fetched data, a hard disk drive unit (HDD) 110 for storing the compressed data, a program 111 stored in the memory of the personal computer 102 which controls the operation of the personal computer 102, a display unit 112 which displays image data before and after the data are fetched into the personal computer 102, and an outputting apparatus 113 for outputting audio data.
The video board 107 is a hardware element for receiving video data inputted from the external apparatus 103 and storing the received data into a memory area which can be accessed by the personal computer 102.
If start and end times of a scene to be fetched are set by an operator and then an execution instruction is issued, the program 111 controls the external apparatus 103 to first shift the read point to the start time and then successively fetch video data successively feeding each frame of video data so that the fetched video data can be compressed and stored until the end time comes.
Then, in order to fetch analog audio data, the read point is shifted to the start time again and then a reproduction instruction is issued to the external apparatus 103, whereafter a recording instruction is issued to the audio board 108 so that fetched audio data are temporarily stored in a storage medium until the end time comes. Then, after the fetching is completed, the steps of reading in, compressing and storing are performed again. Thereafter, the tops of the compressed video and audio data are adjusted to each other to establish a relation between them in terms of time.
Problems of the conventional video and audio editing system described above will be described below with reference to a time chart for the fetch processing of the analog audio data of FIGS. 11(a) and 11(b). FIG. 11 (a) illustrates analog audio data fetch processing when reproduction is performed after recording, while FIG. 11(b) illustrates analog audio data fetch processing when recording is performed after reproduction. Each arrow mark in FIGS. 11(a) and 11(b) represents a route of issuance of an instruction, and the axis of abscissa represents the time.
Referring first to FIG. 11(a), when a recording instruction is first issued to the audio board 108 and then a reproduction instruction is issued to the external apparatus 103 based on the program 111, the following time lags 1, 2, 3 and 4 must be taken into consideration:
1 a time lag after a recording instruction is issued based on the program 111 until the audio board 108 receives the instruction; PA1 2 another time lag after the audio board 103 receives the instruction until it operates, PA1 3 a further time lag after a reproduction instruction is issued based on the program 111 until the external apparatus 103 receives the instruction; and PA1 4 a still further time lag after the external apparatus 103 receives the instruction until it operates.
Due to the time lags, the time at which the audio board 108 actually starts recording is later at a time A than the set start time; the time at which data are inputted to the audio board 108 is later at a time B than the start time; and the time at which recording is ended is later at a time C delayed from the set end time. Consequently, the audio board 108 fails to fetch the audio data from the start time to the time A, and the audio data from the time A to the time B exhibit silence (absence of sound). As a result, when the compressed video and audio data are reproduced simultaneously, the sound is reproduced earlier than the image.